VOICE LESSON: Roseanna Monk says she and her little girl, Genevieve, were the victims of a terrifying tirade by singer Patti LaBelle. (David McGlynn)

That was a costly temper tantrum.

Disco diva Patti LaBelle belted out a profane tirade against a pregnant mom and her little girl in the lobby of a Manhattan apartment building — and now, she has agreed to pay for it to the tune of $100,000, the plaintiff’s lawyer told The Post yesterday.

The Grammy-winning singer allegedly shouted the F-word, called mom Roseanna Monk a “c–t,” and drenched her with bottled water after complaining that Monk’s then-18-month-old daughter was playing near the lobby door of an Upper West Side apartment building where LaBelle was staying in 2010.

When Roseanna — by then cradling her tot, Genevieve, in her arms — accused the “Lady Marmalade” singer of making the girl hysterical, an enraged LaBelle then allegedly had to be held back by her entourage and hustled into a waiting car.

Roseanna and hubby Kevin Monks’ lawyer, Sam Davis, said LaBelle opted to settle the case before even being deposed.

He noted the difficulty that LaBelle would have faced at trial, when he would have brought the adorable little girl into court and said, “That mean woman over there, with the 300-pound bodyguard, was yelling at her.”

“The jury would be shaking their heads,” he said.

Roseanna, a former kindergarten teacher, said all proceeds will be donated to the Hope & Heroes Children’s Cancer Fund.

“This is an opportunity for Patti LaBelle to help a lot of children, and I feel good about that,” she said.

The Nov. 10, 2010, incident took place while LaBelle was renting a Trump Place apartment for her three-month, $50,000-a-week appearance in the Broadway musical “Fela!”

Court papers said the child, now 3 1/2, has suffered “personality changes, sleep disorder” and “increased fear of strangers.”

After the suit wound up in Manhattan federal court last year, LaBelle denied that she was “liable in any way for any alleged claims of injury” and said the Monks were “more than 50 percent at fault.”